The present invention relates to a detection unit, comprising a support element and at least one module connectable to the support element, each module comprising a housing and an infrared detector fitted therein. Such a detection unit is known from the European patent application EP-A- 0 323 621.
In the case of the detection units known in practice, which are used, in particular, in security installations, in general one or two infrared detectors are fitted in a housing. The detection unit is placed in a space that is to be protected, in such a way that the detection range of these infrared detectors will cover part of the space to be protected. Infrared-radiation, which may for example originate from persons present in the space, is detected by a detector if the radiation source (person) is within the detection range of the detector. To protect the whole space it is generally necessary to place several detector units within the space, since only then will the whole space be covered by the detection units.
For the fitting of detection units in different positions within the space, for example in several corners of this space, different detection units are often required. For different locations, detection units with an adjusted detection range (angle coverage) will usually be required. If the unit is placed in the corner of the space, a detection range of, for example, 90.degree. will be required, while for positioning against a plain wall a detection range of 180.degree. will be desirable. Thus, different versions of the detection units have to be produced for different applications. This increases the cost price of such detection units.
The detection unit known from the above-mentioned European patent application is provided with modules, which are connected to the common support elements by means of hinges. These hinges provide two axes of rotation, thus making it possible to vary the orientation of the modules. Although such an arrangement is flexible, due to this largely arbitrary directing of the modules the unit provides no spatial information regarding a detection, i.e. the unit is not possible to determine by means of the detection signals produced by the modules in which part of a space a certain radiation source (e.g. an intruder) is situated. In order to detect an intruder who is situated underneath this known detection unit it is possible to point one of the modules downwards to a certain extent, that as any detector can be bent downwards, a "downward" detection signal cannot be distinguished from any other detection signal. Thus it is not clear whether a detection has been made in the "downward" range or in one of the "horizontal" detection ranges. Furthermore, it is likely that during use the friction of these hinges will diminish, resulting in unwanted changes in the detection range of this known detection unit due to gravity or vibrations.